Education Minister Hekia Parata has agreed not to proceed with any irreversible merger plans ahead of a High Court challenge by Phillipstown School.

She announced on Wednesday the school would be merged on the Woolston School site from January 2015, despite an 18-month legal wrangle and opposition from the Phillipstown community.

The decision is to be challenged by Phillipstown School through the High Court for a second time, after Justice John Fogarty ruled after an October judicial hearing that Parata's consultation in her original decision was unlawful.

Phillipstown's lawyer Mai Chen said Parata's lawyers had agreed to "delay and defer the appointment of the change manager" until the end of July.

If the challenge had not been heard and a High Court judgment delivered by then, the minister would consider a further extension, she said.

The merger decision had already been officially gazetted, but it could always be revoked, Chen said.

Parata's spokeswoman said other merger plans would continue, but "nothing that is irreversible".

She disagreed it was a delay or deferment of the decision.

"The decision stands. We're still heading for January 2015."

The change manager, who works with families and pupils to see them through the changes, and a residual agent, who helps with the school closing down process, would not be appointed at the school until after any potential judicial review. They would, however, be at Woolston.

Advertising for a new principal and setting up an establishment board would continue as planned, she said.